三维有序大孔钙钛矿型氧化物LaFeO3的合成及甲烷化学链重整性能

采用无皂乳液聚合法制备了聚苯乙烯(PS)聚合物微球,并采用胶晶模板法制备了三维有序大孔3DOM LaFeO₃钙钛矿型氧化物.通过扫描电镜、X射线衍射和傅里叶变换红外光谱等手段对氧化物的性能进行了表征.利用程序升温还原和多次氧化还原循环反应评价了氧化物的反应性,并在固定床反应器上研究了其甲烷氧化性能.结果表明,与离心法和蒸发法相比,垂直沉积法获得的PS微球模板排列更均匀有序;前驱物溶剂及浓度对最终的三维有序大孔材料的结构有显著影响,利用乙醇为前驱物溶剂所制备的样品比利用乙烯为溶剂的样品具有更好的三维有序大孔结构,前驱物乙醇溶液浓度在1.0 mol/L为宜.甲烷氧化实验表明,3DOM-LaFeO₃钙钛矿型氧化物中存在两种氧物种:表面吸附氧和体相晶格氧.表面吸附氧主要在反应初期将甲烷完全氧化为CO₂和水蒸汽,而体相晶格氧主要将甲烷部分氧化为H₂和CO.在甲烷部分氧化反应中,三维有序大孔LaFeO₃钙钛矿型氧化物比相同质量的纳米LaFeO₃氧化物提供了更多的氧,并且可使甲烷在较宽的反应阶段生成H₂和CO摩尔比为2:1的合成气,从而更有利于后续的费托合成等工艺.

Synthesis of three-dimensionally ordered macroporous LaFeO3 perovskites and their performance for chemical-looping reforming of methane

Three-dimensionally ordered macroporous (3DOM) LaFeO₃ perovskite-type oxides were synthesized using a polystyrene colloidal crystal templating method. The obtained 3DOM LaFeO₃ was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The reactivity of the perovskite-type oxides was evaluated using temperature-programmed reduction and multicyclic redox reactions by exposing them to an alternating methane and air atmosphere. The methane oxidation performance of the oxides was investigated in a fixed-bed reactor. The effect of the self-assembly method on the structure of the polystyrene template was also studied. A vertical deposition method yielded a more uniform and orderly polystyrene template than those obtained by centrifugation and evaporation techniques. The solvent and concentration of the precursor solution were the major factors to affect the prepared 3DOM perovskite. SEM analysis showed that samples synthesized with ethanol precursor solvent exhibited a better 3DOM structure than those produced with ethylene glycol, and that 1.0 mol/L may be an optimal precursor solution concentration. XRD and FTIR results suggested that the obtained 3DOM LaFeO₃ was pure crystalline perovskite. Two kinds of oxygen species were found to exist on the 3DOM perovskites: surface adsorbed oxygen and bulk lattice oxygen. The surface oxygen contributed to the complete oxidization of methane to CO₂ and H₂O because of its higher reactivity, while the bulk lattice oxygen tended towards partial methane oxidation to H₂ and CO. The available oxygen in the 3DOM LaFeO₃ was higher than that of the same mass of non-3DOM LaFeO₃ during the partial oxidation of methane. Methane was partially oxidized into syngas with a H₂/CO ratio of around 2:1 in a wide time range of the reactions. The generated H₂/CO = 2 syngas was suitable for subsequent gas-to-liquids processes, such as Fischer-Tropsch and/or methanol synthesis.